Sour cream and pastry flour give this coffee cake a light texture.
I got just the right texture when I used 240 grams (8 1/2 oz) of pastry flour. All-purpose and cake flour will work, but the results might be a little different. The key is to use 240 grams or 8 1/2 oz. If you don't have a scale and you are using cake flour, that would be 2 cups and 2 tablespoons. If you are using all-purpose flour (which is a little bit heavier), that would be about 1 3/4 cups plus 2 tablespoons. Of course volume is never really precise so it's hard to say.